1. Field of the Invention
The present invention relates to a scanning device, and more particularly, to a scanning device capable of reducing document scanning times.
2. Description of the Prior Art
Scanning devices, such as fax machines, scanners, copiers, or multi-function products with integrated print, scan and faxing functions, are popular electronics devices. These devices have a scanning device for obtaining a corresponding image from a document.
Please refer to FIG. 1, which is a block diagram of a conventional scanning device 10 according to the prior art. The scanning device 10 comprises a cover 11, a housing 12, a cold cathode fluorescent lamp (CCFL) 14, a photosensor 16 and a controller 18. The CCFL 14 is used for producing light. The photosensor 16, which can be a Charge-Coupled Device (CCD), is used for detecting light produced by the CCFL 14 that reflects off of a document 15. The controller 18 is used for controlling internal operations of the scanning device 10.
The basics of the scanning device 10 are described as follows. First, the desired document 15 is placed onto the scanning device 10 and the cover 11 is closed, which prevents ambient light from influencing the scanning process. Then, the CCFL 14 generates light to illuminate the document 15, and the photosensor 16 detects the reflected light from the document 15. Since less light is capable of being reflected from dark areas of the document 15, while more light is reflected from the bright areas of the document 15, the photosensor 16 is able to detect the corresponding intensity variations of the reflected light. Finally, the controller 18 transforms the detected intensity patterns of the reflected light into digital data, and combines these digital data into an image file.
Please refer to FIG. 2 in conjunction to FIG. 1. FIG. 2 illustrates a relationship between intensity variations of the cold cathode fluorescent lamp versus time during a warm-up time period. Color image information is obtained by using the CCFL 14 of the scanning device 10 to scan a single time, and this is possible when a sufficiently stable and bright light is produced by the CCFL 14. To do so, the CCFL 14 must reach a sufficiently high temperature to excite enough ions to strike the fluorescent material disposed on the glass tube of the CCFL 14. In general, the period required to heat the CCFL 14 to the appropriately high temperature is called the warm-up time period. A so-called warm-up time period(t0˜t1), with values of 45 to 90 seconds, is typically required. During the warm-up time period, a substantial luminance variation of the light provided by the CCFL 14 is exhibited. If the luminance variation is too great, corresponding errors for the reflected light detected by the photosensor 16 are created. From FIG. 2, the luminance variation of the light provided by the CCFL 14 in the period between t0-t1 is too great to permit color scans. As an example, during the period of ta˜tb as illustrated in FIG. 2, when using the CCFL 14 to scan the area 17 of the document 15 having a uniform gray level, ideally the photosensor 16 should detect the same reflected light luminance. However, because the luminance of the light provided by the CCFL 14 at the time tb is larger than that at the time ta, the photosensor 16 detects a different luminance for the same gray-level area 17, causing the controller 18 to read error-laden data, which leads to incorrect image data. Hence, the CCFL 14 of the conventional scanning device 10 requires a relatively long warm-up time for generating a sufficiently stable and bright light to ensure a high quality scan.
To reduce scanning times while maintaining high quality scans, the scanning device 10 may be provided more than one CCFL 14. In this way, higher light intensities are available, but the warm-up time period remains unchanged. This is a waste of time for the user.